1. Field of the Invention
The present invention relates to a method and apparatus for determining image quality. More particularly, the present invention relates to a method, apparatus and computer program product for determining the quality of images which have been scanned using imaging apparatus, such as a document scanner.
2. Description of Related Art
Image processing has burgeoned in the last several years. The advent of powerful, yet relatively low cost, computers have ushered in a variety of image processing applications. For example, documents can now be scanned, converted to digital form, and manipulated in a number of ways for various purposes. The United States Patent Office's Automated Patent System (APS) stores certain patents in digitized form for search and retrieval purposes. Banks routinely process checks and other financial instruments based on information gleaned from a digital image of a document. The availability of low cost desktop and handheld scanner devices has also precipitated image processing by individuals and small businesses.
As users of image processing place more and more reliance on the technology, the need to ensure quality becomes acute. In general, the quality of an imaging system can be monitored by examining either the system itself or the product of the system (i.e., the digital image produced by the system). The system itself can be monitored by examining responses received from control points within the system, such as hardware or software components. Unfortunately, the following types of quality problems may not be detectable by examining system control points:
dust accumulation in the illumination and imaging system(s) or other optical or electronic defocus; PA1 bad CCD, photo diode element(s), or picture element(s) (pel(s)); PA1 analog processing failures; PA1 loose cables/connections, and defective components; PA1 analog/digital conversion failures due to circuit failures or maladjusted reference points; and PA1 data path problems due to shorts/opens on printed circuit cards in areas where standard techniques such as parity and checksums are not employed.
Since these problems may not be detectable by examining the system control points in the system, unacceptable images may not be detected until the problem is discovered visually by an end user. It is important to detect and report these problems as soon as they occur. This is especially true in a high speed scanner application (e.g., image processing of bank checks) since the end user cannot monitor the scanner output quality in real time.
A typical technique for determining problems is to present a test target to the scanner and analyze the scanner output. The problem is that this interferes with normal use of the scanner and reduces scanner throughput. Some known techniques (e.g., histogram analysis) attempt to overcome this problem by analyzing scanner output to determine if one gray level is more prevalent in the image that any other. Since these techniques make assumptions about the type of document that will be scanned (e.g., multi-shade or color document), they are only useful for certain applications (e.g., diagnostic mode testing). These techniques are also insensitive to isolated pel failures.